The present invention relates to a cap assembly of a battery, and more particularly, to a cap assembly of a battery which can effectively discharge a gas generated within the battery.
FIG. 1 is an example of a conventional battery having a hexahedral rubber member. The battery has a cylindrical case 20 in which a roll of anode and cathode plates 21 and 22 having a separator 23 intervened therebetween is placed. The separator 23 insulates the plates 21 and 22. A cap assembly 10 including a cap 12 having a rubber member 14, and a cap cover 11 is installed on the upper portion of the anode and cathode plates 21 and 22. A gasket (not shown) is installed around a portion where the cap 12 contacts the cap cover 11 such that the anode and cathode are insulated and an electrolytic solution is prevented from leaking, to thus protect the battery.
The battery generates electricity through a chemical reaction which causes electrons to flow from the cathode to the anode. When an overcharge occurs, a gas is greatly generated which sharply increases the internal pressure of the battery.
The increase of internal pressure in the battery may cause the case 20 to explode. The cap assembly 10 including the rubber member 14 is installed to prevent the explosion. When the pressure inside the case increases to a predetermined level, the rubber member 14 covering a gas discharge hole 13 of the cap cover 11 becomes separated from the cap cover 11, thereby opening the gas discharge hole 13 to discharge the gas, which prevents the case 20 from exploding.
FIGS. 2, 3 and 4 show different types of conventional rubber members for the cap assembly of the battery shown in FIG. 1, wherein (a) is a sectional view and (b) is a plan view.
FIG. 2 shows a hexahedral rubber member, FIG. 3 shows a hat-shaped rubber member having a cylindrical head, and FIG. 4 shows a rubber member assembly constituted by a spring, a steel plate, and a rubber element.
The rubber member inclines while being inserted into the cap assembly. At this time, if the rubber member inclines to one direction in the cap assembly, a deviation of pressure applied to the bottom portion is generated. Thus, it is natural that, a portion to which less pressure is applied, is more easily lifted. Accordingly, more gas is discharged through the portion to which less pressure is applied.
Such a phenomenon causes a reduction in the durability of the battery by partially curing the rubber member. When the partial cure of the rubber member and the reduction of the battery life become serious with the increase in the deviation of pressure, an appropriate adjustment of pressure deviation is very important to improve the quality of the battery.
In general, it is preferable that the deviation of pressure applied to the bottom surface of the rubber member should be adjusted within the range of 15.+-.2 kgf/cm.sup.2.
However, in the case of the hat-shaped rubber member having a cylindrical head or the hexahedral rubber member, a force is not applied uniformly to the bottom surface because of the inclination generated when inserted into the cap assembly, so that the pressure deviation problem becomes more serious.
That is, as shown in FIG. 5(a), if the hexahedral rubber member is biased toward the left side while being inserted into the cap assembly, a force is prone to concentrate only on the lower surface of the left side. This tendency is represented by an arrow.
Also, as shown in FIG. 5(b), if the hat-shaped rubber member having a cylindrical head is biased toward the left side, a force is applied toward the left side, not uniformly applied to the bottom surface of the rubber member. This phenomenon is represented by an arrow.
If a force is biased toward one side, a great amount of gas is discharged through the other side to which relatively less force is applied. Thus, a portion through which a lot of gas is discharged starts being cured earlier than the other portion.
Meanwhile, there is no inclining problem in the rubber member assembly composed of the spring, steel, and rubber element shown in FIG. 4. However, since the above rubber member assembly should be assembled using three different components, it takes many steps and much cost to manufacture the rubber member assembly. Furthermore, the above rubber member assembly is not suitable for a cap assembly of a high voltage battery which generates a lot of gas, due to the elastic limit of the spring.